The present invention relates to methods and arrangement in a base station in mobile telecommunication network having at least two arbitrary communication channels, e.g. a data channel and an associated control channel, which share a common resource where the timing of resource sharing is overlapping.
An example of such a mobile telecommunication network is a UMTS terrestrial radio access network (UTRAN). The UTRAN is illustrated in FIG. 1 and comprises at least one Radio Network System 100 connected to the Core Network (CN) 200. The CN is connectable to other networks such as the Internet, other mobile networks e.g. GSM systems and fixed telephony networks. The RNS 100 comprises at least one Radio Network Controller 110. Furthermore, the respective RNC 110 controls a plurality of Node-Bs 120,130 that are connected to the RNC by means of the lub interface 140. Each Node B, also referred to as base station, covers one or more cells and is arranged to serve the User Equipment (UE) 300 within said cell. Finally, the UE 300, also referred to as mobile terminal, is connected to one or more Node Bs over the Wideband Code Division Multiple Access (WCDMA) based radio interface 150.
Requirements for mobile data access are increasing and demand for higher bitrates is growing. To meet these needs the HSDPA specification has been defined. HSDPA is based on WCDMA evolution standardized as part of 3GPP Release 5 WCDMA specifications. HSDPA is a packet-based data service in WCDMA downlink with data transmission peak rate up to 14.4 Mbps over a 5 MHz bandwidth. Thus HSDPA improves system capacity and increases user data rates in the downlink direction. The improved performance is based on adaptive modulation and coding, a fast scheduling function and fast retransmissions with soft combining and incremental redundancy. The adaptive modulation and coding makes it possible to adapt the modulation scheme and coding according to the quality of the radio link. The fast scheduling function of the transmission of data packets over the radio interface is performed in the base station based on information about the channel quality, terminal capability. QoS class and power/code availability. The scheduling is denoted fast because it is performed as close to the radio interface as possible and because a short frame length is used. Fast retransmission implies that the requests for retransmission are performed by the base station instead of the Radio Network Controller (RNC) as in traditional WCDMA systems. By implementing the retransmission function in the base station instead of the RNC it is possible to achieve a faster retransmission.
HSDPA utilizes a transport channel named the High Speed Downlink Shared Channel (HS-DSCH) that makes efficient use of valuable radio frequency resources and takes bursty packet data into account. This is a shared transport channel which means that resources, such as channelization codes, transmission power and infra structure hardware, is shared between several users. When one user has sent a data packet over the network, another user gets access to the resources and so fourth. In other words, several users can be time multiplexed so that during silent periods, the resources are available to other users. On the other hand, several users can share the resource simultaneously by code multiplexing. Furthermore, HSDPA utilizes a control channel named the High Speed Shared Control Channel (HS-SCCH) that serves the purpose of informing which UE that is to receive the HS-DSCH in the next time period. The HS-SCCH also tells the scheduled UE about transmission parameters of the HS-DSCH.
The HS-SCCH channel has fixed control information content and thereby, the required transmission power needs to be adjusted according to the radio channel quality to be received by the UE. The HS-DSCH has variable payload information content for best effort data and the amount of data is adapted to the available power and radio channel quality.
The transmission time in a WCDMA system is divided into Transmission Time Intervals (TTIs). The TTI length for the HS-DSCH equals 2 ms and a TTI is divided into three slots as shown in FIG. 2. The timing for the High Speed Shared Control Channel (HS-SCCH) is two slots ahead of the HS-DSCH for a particular UE. That depends on that information such as transport format, UE identity and channelization code set is sent on the HS-SCCH in order to prepare the UE for receiving data on the HS-DSCH.
Due to the staggered timing of the High Speed Downlink Shared Channel (HS-DSCH) and the High Speed Shared Control Channel (HS-SCCH) transmissions as shown in FIG. 2, the base station usually adopts a relatively conservative solution when the available power for the HS-DSCH is estimated by assuming that the HS-SCCH transmission for the next TTI will be the maximum allowed HS-SCCH power. Thus, resources may be wasted (denoted wasted resource) if the maximal allowed HS-SCCH is not required to be used shown in FIG. 2. It should be noted that this application relates to the case when the HS-SCCH power is set individual for each UE.
An alternative solution is to use the actual left power for the HS-DSCH, and not to assume that the maximal HS-SCCH power is used. However in this solution, there is a risk that the total power level exceeds the available total power level due to the staggered timing of HS-DSCH and HS-SCCH. I.e. the selected power of the HS-DSCH for a first scheduled UE together with the HS-SCCH power of a subsequently scheduled second UE may exceed the available HS power. This overbooking is illustrated in FIG. 3. Due to the risk of overbooking the downlink, power limiting functions in the base station will usually reduce power for all channels (including common control channels and traffic channels) and eventually degrade the quality of all on going connections in the cell.
The problem with the trade-off between overbooking risk vs. under utilization of power will increase in the case of code multiplexing. I.e. a multiple of users are code-multiplexed onto the same TTI. In that case there is one HS-SCCH for each multiplexed user. Thus, it will be a large waste of power to reserve the maximal HS-SCCH power times the maximal number of multiplexed users. The potential resource waste is illustrated in FIG. 4.